1. Field of the Invention
The present invention relates to metal-clad moldings of thermoplastic resins and to a process for manufacturing the same. Particularly, the invention relates to such thermoplastic resin articles formed by injection molding and to a process comprising injection molding for manufacturing those articles.
2. Description of the Prior Art
It is already well-known that PWBs or substrates are made of thermoplastics, so called high temperature thermoplastic resins, such as polyether-sulfone and polyetherimide, by injection molding. The process currently being promoted to place conductors on such boards or substrates include (1) an electroless plating process, (2) employing electroconductive coating process, (3) a thermal transfer process, and (4) in-mold transfer process (Japanese Patent Application Kokai No. 57-7193). However, each of these process involves problems, which are, for example, the following:
As to the electroless plating process, conductors of 18 to 35 .mu.m in thickness are difficult to form, the process is complicated, e.g. various washing steps are required, and the technology to permit imaging on a three-dimensional shape is not established.
In the case of the electroconductive coating process, the reliability of placed conductors is unsatisfactory, for instance, the resistance of conductive traces is not unifom the circuits on exposure to heat cycles are liable to break, as well as liable to crack upon exposure to heat cycle, and printing on a three dimensional shape is also difficult.
The thermal transfer process has the same problems as electroconductive coating process has, and transferring conductive traces onto three-dimensional substrates is limited in their abilities to produce conductive features.
In addition to these problems, above three process, in common, tend to include many operation steps and hence the production costs go up higher.
On the other hand, in the in-mold process, thermal transfer paper, onto which the conductive traces are printed previously, is set in a mold die.
A plastic molding composition is injected into the mold cavity and comes into contact with and adheres to the conductive trace, at the same time the substrate is injection-molded. Hence, the in-mold process can get rid of many separate steps circuits on a substrate and is quite fitted for mass production. However, in case of high temperature thermoplastic resins, the conductive traces tend to be damaged or poor in adhesion because of the higher resin temperature and the higher injection pressure. Although copper foil circuits, on the other hand, could be formed with ease in this process by conventional etching process and the damage of the circuits themselves thus can be avoided, the adhesive strength of copper foil circuits to molded substrates is very low; hence this process employing copper foils has not been put to practical use.
That is, when copper foil circuits are formed on injection-molded substrates of high-temperature resins such as polyethersulfone and polyetherimide according to the in-mold method by employing thermal transfer films, the copper foil circuits will have little adhesive force to the molded substrates. Therefore, it has been impossible up to now to apply such moldings as printed circuit boards or substrates.